Benzene nickel complex

Upon treatment with suitable cobalt complexes, methylbutynol cyclizes to a 1,2,4-substituted benzene. Nickel complexes give the 1,3,5-isomer (196), sometimes accompanied by linear polymer (25) or a mixture of tetrasubstituted cyclooctatetraenes (26). 

Cyclization with various nickel complex catalysts gives up to 97% selectivity to a mixture of cyclooctatetraene derivatives, with only 3% of benzene derivatives. The principal isomer is the symmetrical l,3,5,7-cyclooctatetraene-l,3,5,7-tetramethanol (29). 

Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

Biaryl synthesis from aryl halides is a more interesting reaction due to the value of these molecules and their difficult access by chemical methods. The first electrosyntheses were simultaneously done in 1979-80 by three groups [21-23] who used NiCljPPha (1-20%) as catalyst precursor in the presence of excess PPhs. Later, several groups investigated the use of bidentate phosphines like dppe associated with nickel in the synthesis of various biaryls, and notably 2,2 -bipyridine and of 2,2 -biquinoline from respectively 2-chloropyridine and 2-chloroquinoline [24], More recently new nickel complexes with l,2-bis(di-2-alkyl-phosphino)benzene have been studied from both fundamental and synthetic points of view [25]. They have been applied to the coupling of aryl halides. 

Intramolecular cross-coupling can also be carried out as illustrated in the ring closure of Eq. 6 catalyzed by a nickel complex (L = l,2-bis-(diisopropyl phosphino)benzene) [25] ... 

Finally, a few cyclizations of unsaturated side chains on o-halogeno-anilines or -benzenes have been catalyzed by transition metal complexes. Cyclization of the cinnamylbenzylamine (245) by palladium gives some 4-benzylisoquinoline and some of compound (246) (77TL1037). Acryloylanilines (247) and (248) can be cyclized by a nickel complex (75MI20800) or by a palladium complex (79JA5281). The mechanism for the latter reaction is given in equation (50). 

C18H18, Benzene, l,3-butadiene-l,4-diyl-bis-cobalt complex, 26 195 C,8H33P, Phosphine, tricyclohexyl iron complex, 26 61 nickel complexes, 26 205, 206 C H 7OP, Benzenemethanol, 2-(diphenyl-phosphino)-... 

Thioethers (sulfides) can be prepared by treatment of alkyl halides with salts of thiols (thiolate ions).7S2 R may be alkyl or aryl. As in 0-35, RX cannot be a tertiary halide, and sulfuric and sulfonic esters can be used instead of halides. As in the Williamson reaction (0-12), yields are improved by phase-transfer catalysis.753 Instead of RS ions, thiols themselves can be used, if the reaction is run in benzene in the presence of DBU (p. 1023).754 Neopentyl bromide was converted to Me3CCH2SPh in good yield by treatment with PhS in liquid NH3 at -33°C under the influence of light.755 This probably takes place by an SrnI mechanism (see p. 648). Vinylic sulfides can be prepared by treating vinylic bromides with PhS in the presence of a nickel complex,756 and with R3SnPh in the presence of Pd(PPh3)4.757 R can be tertiary if an alcohol is the substrate, e.g,758... 

Using standard anaerobic techniques, a 100-mL Schlenk flask equipped with a stir bar is charged with 50 mL dry benzene and 2 mL (1.96 g, 0.0172 mol) distilled free amine. If crude daco is used, the product will be less pure and of lower yields. The mixture is warmed to 50-60°C under N2. Three 1-mL (0.05 mol) portions of ethylene sulfide are added, allowing 20 min reaction time between additions. The mixture is then heated under N2 for 1 h. Complete reaction is indicated by the formation of a finely divided white precipitate after the final addition. The reaction mixture is filtered anaerobically through a bed of celite in a glass-fritted funnel. Solvent is removed under vacuum while continuing to heat at 50-60°C. The H2-bme-daco is obtained as a colorless to pale yellow oil. Irrespective of color, this material is of suitable quality to be converted to the nickel complex. If distilled daco is used, the product is quite pure. Attempts at vacuum distillation (bpo.immHg = 135°C) resulted in partial decomposition. Yield 3.21 g (80%). 

Tolman has shown that the equilibrium constants for the reactions of 38 substituted ethylenes with Ni[P(0-o-tolyls)]3 in benzene, to form (ENE)bis-(tri-o-tolylphosphite)nickel complexes, is sensitive to the ethylene s structure, eqn. (2) (ref. 7). Values of Ki at 25° vary from 10 for cyclohexene to... 

Copper and nickel complexes of the tridentate l-(2-carboxyphenyl)-3,5-diphenyl- (169 X = C02 R = R = Ph) and 1-(2-hydroxyphenyl)-3,5-diphenyl-(169 X = 0 R = R = Ph) formazans were prepared118 by the interaction of the formazan and the appropriate metal acetate in alcohol and were assigned the three-coordinate structures (170 X = O, C02 R = R = Ph M = Ni, Cu) since the diamagnetic nickel complexes were found to be unimolecular in benzene solution. Treatment of the nickel complex (170 X = O, R = R = Ph M = Ni) with pyridine gave a violet crystalline adduct which was assigned the four-coordinate structure (171 X = O R = R = Ph M = Ni). A product similar to the latter could not be obtained from the nickel complex of l-(2-carboxyphenyl)-3,5-diphenylformazan but nickel complexes of this type were obtained from both l-(2-hydroxyphenyl)- (169 X = O, R = CN R = Ph) and l-(2-carboxyphenyl)- (169 X = C02 R = CN R = Ph) 3-cyano-5-phenylformazans. In all three cases a considerable shade change occurred on going from the three-coordinate complex to the pyridine adduct. 

The above study has been extended to the synthesis of 4 which was prepared in a similar fashion to 1 and 3 starting from tris(l,4,7-triazacyclonon-l-ylmethyl)benzene [12], The X-ray structure of the [Ni2(4)(H20)3]4+ cation shows that both nickel ions adopt distorted octahedral coordination geometries, with one nickel being sandwiched between two tacn residues while the other is coordinated to the third tacn residue with the coordination sphere being completed by three water ligands. Electrochemical studies indicate that the sandwiched Ni(II) centres in this and the related nickel complexes mentioned above may the be reversibly oxidised to the Ni(III) state. In the case of the dinuclear bis-sandwich complex, [Ni2(4)](C104)4, the electrochemical results indicate that the two nickel centres behave in an essentially independent manner. 

Sato and coworkers [137] reported the synthesis of macrocyclic lactones via intramolecular alkylation of n-allylic nickel complexes, based on the facile reactivity of n-allylic nickel complexes toward alkyl halides. As shown in Scheme 75, this method was applied to the synthesis of the macrolide recifeiolide 227). The linear precursor 226 in benzene was added slowly over 1 h to nickel carbonyl in benzene at 50 °C. After additional 1.5 h at 50 °C, 227 was obtained in 32% yield. 

Tolman has shown that the equilibrium constants for the reactions of 38 substituted alkenes with Ni[P(0-o-tolyl)3]3 (13) in benzene, to form (ENE)bis(tri-o-tolylphosphite)nickel complexes (14), are sensitive to the structure of the alkene (equation 13). Values of K[ at 25 °C vary from 10 to 4 x 10. The stability of the complex is enhanced by electron-withdrawing substituents such as cyano and car-boxy and lowered by alkyl groups. That resonance involving unshared electrons on the oxygen of an al-koxy group overpowers the inductive effect is indicated by the relative values of Ki for allyl methyl ether, 1-hexene and vinyl butyl ether which diminish in that order by factors of 3 1 0.006. 

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